Heat-sensitive recording materials that take advantage of a color forming reaction between an electron-donating compound and an electron-accepting compound are relatively inexpensive. Recording devices for such heat-sensitive recording materials are compact and their maintenance is easy. Therefore, such heat-sensitive recording materials have been used in a broad range of technical fields, for example, as recording media for facsimiles, word processors, computers, video cassette recorders, medical images and other applications.
Recently, there has been an increasing demand for the development of heat-sensitive recording materials having excellent transparency and image quality for use as substitute recording media for silver halide films for recoding medical images, typically radiographs for medical images. However, heat-sensitive recording materials, in which a heat-sensitive recording layer has been formed on a transparent film to enhance transparency and image quality, suffer blocking, when exposed to high humidities, due to adhesion of the front side and backside thereof, particularly when they are used in the form of a roll.
Such a heat-sensitive recording material in which a heat-sensitive recording layer is formed on a transparent film is disclosed in Japanese patent No. 2761985, in which a heat-sensitive recording material comprises a heat-sensitive recording layer on one side of the transparent film, and an antireflective layer containing a binder and a pigment with a particle diameter of 7.5 to 50 μm on the other side. The object of this patent is to enhance the image quality by providing such antireflective layer to thereby reduce glitter that occurs when the heat-sensitive recording material is viewed through its support, and the patent does not disclose the problem of preventing blocking or a means for solving the problem.
Also known is a heat-sensitive recording material which comprises, on one side of a transparent film, a heat-sensitive recording layer and a protective layer mainly containing a resin and a filler and formed on the heat-sensitive recording layer, and, on the other side of the transparent film, an antistatic layer containing a binder, fine spherical resin particles having a particle diameter of about 1 to about 6 μm and an antistatic agent (Japanese Unexamined Patent Publication No. 1998-193796). This patent publication describes that, due to the use of the fine spherical resin particles and the antistatic agent such as a conductive metal oxide in the antistatic layer, this heat-sensitive recording material allows smooth feeding within recording devices, forms dimensionally accurate images, prevents dust accumulation, and prevents blocking. However, such heat-sensitive recording material, when exposed to high humidities, sometimes suffers blocking because of adhesion of the front side and backside.